`a, (2\sqrt{2} - \sqrt{5} + \sqrt{18}).(\sqrt{50} + \sqrt{5})`

`= (2\sqrt{2} - \sqrt{5} + 3\sqrt{2}).(5\sqrt{2} + \sqrt{5})`

`= (5\sqrt{2} - \sqrt{5}).(5\sqrt{2} + \sqrt{5})`

 `= (5\sqrt{2})^2 - (\sqrt{5})^2`

`= 50 - 5`

`= 45`
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`b, 1/(\sqrt{3} - \sqrt{2}) - 1/(\sqrt{3} + \sqrt{2}). (2 - \sqrt{2})/(1 - \sqrt{2})`

`= {(\sqrt{3} + \sqrt{2}) - (\sqrt{3} - \sqrt{2})}/(3 - 2).{\sqrt{2}(\sqrt{2} - 1)}/(1 - \sqrt{2})`

`= (\sqrt{3} + \sqrt{2} - \sqrt{3} + \sqrt{2})/1. - {\sqrt{2}(1 - \sqrt{2})}/(1 - \sqrt{2})``

`= 2\sqrt{2}. -\sqrt{2}`
`= - 2.2 = - 4`

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$\text{@Riechannnn}$

$#Rosé$

Đáp án:`+`Giải thích các bước giải:

`a)` 

`(2\sqrt{2}-\sqrt{5}+\sqrt{18}).(\sqrt{50}+\sqrt{5})`

`=(2\sqrt{2}-\sqrt{5}+\sqrt{3^2 .2})(\sqrt{5^2 . 2}+\sqrt{5})`

`=(2\sqrt{2}-\sqrt{5}+3\sqrt{2})(5\sqrt{2}+\sqrt{5})`

`=(5\sqrt{2}-\sqrt{5})(5\sqrt{2}+\sqrt{5})`

`=50-5`

`=45` 

`b)`

`(1/(\sqrt{3}-\sqrt{2})-1/(\sqrt{3}+\sqrt{2})).(2-\sqrt{2})/(1-\sqrt{2})`

`=(\sqrt{3}+\sqrt{2}-(\sqrt{3}-\sqrt{2}))/((\sqrt{3}-\sqrt{2})(\sqrt{3}+\sqrt{2})).(\sqrt{2}(\sqrt{2}-1))/(1-\sqrt{2})`

`=(\sqrt{3}+\sqrt{2}-\sqrt{3}+\sqrt{2})/((\sqrt{3})^2-(\sqrt{2})^2) . (-\sqrt{2}(\sqrt{2}-1))/(\sqrt{2}-1)`

`=2\sqrt{2} . (-\sqrt{2})`

`=-2 . (\sqrt{2})^2`

`=-2.2`

`=-4`